code: def cumsum(field_name: str, include_zero: bool = False) -> Expr:
      """Create a ``DataSpec`` dict to generate a ``CumSum`` expression
      for a ``ColumnDataSource``.
  
      Args:
          field_name (str) : a field name to configure ``CumSum`` with
  
          include_zero (bool, optional) : whether to include zero in the sum
              (default: False)
  
      Examples:
  
          .. code-block:: python
  
              p.wedge(start_angle=cumsum('angle', include_zero=True),
                      end_angle=cumsum('angle'),
                      ...)
  
          will generate a ``CumSum`` expressions that sum the ``"angle"`` column
          of a data source. For the ``start_angle`` value, the cumulative sums
          will start with a zero value. For ``end_angle``, no initial zero will
          be added (i.e. the sums will start with the first angle value, and
          include the last).
  
      """
      return Expr(CumSum(field=field_name, include_zero=include_zero))
  
file_path: bokeh/src/bokeh/transform.py
imports: from __future__ import annotations
  import logging
  from typing import TYPE_CHECKING, Sequence, Union
  from .core.property.vectorization import Expr, Field
  from .models.expressions import CumSum, Stack
  from .models.mappers import CategoricalColorMapper, CategoricalMarkerMapper, CategoricalPatternMapper, EqHistColorMapper, LinearColorMapper, LogColorMapper
  from .models.transforms import Dodge, Jitter
label_desc: Use image node_id 1 for calling a global function with example usage: cumsum(field_name, include_zero) and returns: Expr